Internet protocol is a network layer protocol that is described, for example, in the Internet Engineering Task Force (IETF) technical report RFC 791.
In that protocol, information is transmitted in the form of datagrams each possessing a header containing in particular control parameters, routing parameters, and address parameters (IP addresses) enabling information to be routed between two pieces of network equipment. The routing parameters are contained in a type of service (TOS) field as defined in particular in technical reports RFC 1349 and RFC 1455 which specify the size of the field and the nature of the routing parameters (priority, reliability, quality, . . . ).
There exist airplanes having internal networks that make use of the Internet protocol. Such networks include a secure network used for operating the airplane itself and a public network of servers used in particular by the crew for obtaining information about a flight or passengers, the airports visited, . . . , and also to enable passengers to have access to entertainment means. The public network is not highly secure and it is connected to the secure network via a protection and routing device. The public network may also be connected via a conventional routing device to the Internet.
In order to avoid any possibility of the secure network being disturbed by datagrams coming from non-authorized equipment connected to the network having a low level of security, the protection and routing device is authorized to forward datagrams coming from the non-secure network only if it can itself identify the server that issued the datagram and can determine that the server is indeed one of the servers on-board the airplane.
To do this, a server issuing a datagram can be identified from the IP address of the datagram header or from the media access control (MAC) addresses that belong to each of the interfaces of the network elements and that appear in the network access layer datagram encapsulating the Internet protocol datagram. Nevertheless, when servers have a large number of interfaces designated by static or dynamic IP addresses, it becomes necessary for the protection and routing device connected to the secure network to have a large table associating each server with the IP addresses that correspond thereto. The same applies to the MAC addresses, since the protection and routing device is configured for being installed in a plurality of airplanes, each having its own servers, thus making it necessary for it to include a table containing the MAC addresses of all of the servers with which it might be connected. The use of such tables requires large computer resources that are not available in a protection and routing device connected to the secure network.